Fix compatibility with Python 2.6.1 (Snow Leopard)

This workarounds a bug in Python 2.6.1 that has been fixed in later versions. Since this version is the default one in Snow Leopard system, it makes sense to add a simple, non-invasive workaround.

The bug is that **kwargs wouldn't work with unicode literals, and it's been fixed in Python 2.6.5:
http://bugs.python.org/issue4978